Retaining water in a fuel cell stack for cooling and humidification during frozen startup

Abstract

A fuel cell power plant (19, 19a) has a plurality of fuel cells (70, 70a, 70c) arranged in a stack (20, 20c), each fuel cell having porous, at least partially hydrophilic water transport plates (75, 81) with fuel (74) and oxidant (82) reactant gas channels, there being water channels (78, 85, 78a, 85a, 78c, 85c) exchanging water with the water transport plates. On shut down, water is retained in the water channels and water transport plates by means of either a micro vacuum pump (46), one or two valves (89, 90, 118, 120), a check valve (95, 99), capillary force in the water channels to prevent water from entering the reactant channels which, if frozen, could block flow of reactant gas upon startup.

Description

[0001]This application is based on PCT / US05 / 13040, filed 15 Apr. 2005, having a 371 (c) date of 15 Oct. 2007.TECHNICAL FIELD[0002]This invention relates to fuel cell power plants, such as PEM fuel cell power plants, in which water is retained in the water channels, or other water conduits adjacent to porous, at least partly hydrophilic water transport plates, and in water manifolds interconnected therewith, without allowing water to “droop” into the reactant flow fields or reactant manifolds, thereby to provide both cooling and humidification during a frozen startup without blocking flow of reactant gases to the electrodes.BACKGROUND ART[0003]Fuel cell power plants that provide electricity to the propulsion system of electric vehicles must be operable at temperatures below that at which water will freeze. Traditional methods of operating fuel cells shut down in environments which may reach freezing temperatures involve draining all the water out of the fuel cell into a reservoir of ...

AI Technical Summary

Benefits of technology

[0008]According to the present invention, upon shut-down of a fuel cell stack, in which each fuel cell includes porous, at least partially hydrophilic reactant gas flow field plates (referred to herein as “water transport plates”), water is retained in the water channels and the water manifolds connected thereto in a manner that prevents substantially all of the water from “drooping” through the water transport plates into the reactant gas channels; the effect of the invention is providing water for humidification and cooling at start up, without ice blocking the reactant channels, so that reactant gases will have access to the electrode catalysts.

[0009]According to the invention, water may be caused to remain in the water channels and manifold by capillary pressure, which is controlled by selection of the cross sectional area of the channels, the size of pores if a porous medium utilized instead of channels, or the effective cross sectional flow area of wicking or woven substances should such be used. According to the invention, the capillary rise in round water tubes or pores as a function of the radius of the tubes or pores, can be calculated and thereafter determined from equations, graphs or tables. According further to the invention, the capillary rise of water within porous or woven wicking or water conducting media of any sort is readily determined empirically.

[0010]According to the invention, water may be retained in the water channels of the fuel cell stack during shutdown by means of a micro vacuum pump, such as the type used in small residential fish tanks; the water may be retained in the stack by valves, after which a micro vacuum pump may be shut off; the water may be retained in the stack by means of check valves, including a passive check valve composed of a hydrophobic diaphragm with a freeze proof hydrophobic fluid on top of the layer diaphragm.

[0011]Other objects, features and advantages of the present invention will become more apparent in the light of the following detailed description of exemplary embodiments thereof, as illustrated in the accompanying drawing.

Problems solved by technology

That much of a delay is generally thought to be intolerable in vehicles, which are thought to require at least partial mobility within a few seconds of a start command, such as the turning of a key.

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